1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium suitable for use in a digital video tape recorder (VTR) etc. and a process for the production of the same
Further, the present invention relates to a method of perpendicular magnetic recording and/or reproduction suitable for recording and reproduction of digital signals on a magnetic recording medium of a digital VTR, for example, in particular relates to a method of perpendicular magnetic recording and/or reproduction suitable for compressing and recording digital signals in a manner with little reproduction distortion.
2. Description of the Related Art
In the field of magnetic recording, high densities of recording are demanded each year. Further, the signal format is changing from analog to digital. This has made necessary both higher recording density and the design of a medium which can handle that signal format.
Up until now, the main system of magnetic recording has been so-called in-plane magnetic recording, which uses a magnetic recording medium with an axis of easy magnetization in the plane of the medium. In this system, however, the higher the recording density is raised, the more the directions of magnetization of the magnetic recording medium repulse each other when they are aligned, so there are inherent limits to increasing the recording density and it is difficult to achieve the high recording density demanded.
Further, in the in-plane magnetic recording system, in a pattern where flux inversion is repeated twice, the closer the intervals of the flux inversions (the higher the density), the worse the problems of peak shifts occurring due to mutual magnetic repulsion and waveform interference and the deterioration of the error rate.
In recent years, therefore, a new system of magnetic recording has been developed--the so-called perpendicular magnetic recording system, used for magnetic recording medium having an axis of easy magnetization in a direction perpendicular to the film plane. Great hopes are riding on its commercialization.
In the perpendicular magnetic recording system, the demagnetization action is much smaller than with the in-plane magnetic recording system and the magnetic domains are stable. By using this system, therefore, it becomes possible to strikingly increase the recording density.
As the magnetic recording medium used for the perpendicular magnetic recording system, use has mainly been made of a Co--O type perpendicular magnetic recording medium which has as its magnetic layer a Co--O alloy film etc. formed by vapor deposition.
In such a Co--O type perpendicular magnetic recording medium, the columnar particles of Co are arrayed in a direction perpendicular to the plane of the film covered by an oxide film and the axis of easy magnetization, or the C-axis, is oriented in this direction, so excellent perpendicular recording characteristics are obtained.
In such a perpendicular magnetic recording medium, the crystallinity and orientation of the alloy film have a major effect on the magnetic characteristics of the medium. By controlling well the crystallinity and the orientation, it is therefore possible to obtain excellent electromagnetic conversion characteristics. Therefore, to improve the electromagnetic conversion characteristics, it is desirable to elucidate the crystal structure and magnetic anistrophy of the alloy film and to set the suitable conditions for controlling the same.
On the other hand, digital signals are recorded and reproduced by the perpendicular magnetic recording system using a combination of the above-mentioned perpendicular magnetic recording medium and ring type magnetic heads.
When recording and reproducing rectangular wave signals by a combination of a perpendicular magnetic recording medium and ring type magnetic heads, however, the solitary reproduced wave becomes a dipulse waveform unique to the perpendicular magnetic recording system.
The biggest feature of the perpendicular magnetic recording system is the ability to record at a high density, but if the solitary reproduced wave becomes a dipulse waveform, equalization of the waveform, some change of the signal detection method, etc. become necessary and a circuit system performing more complicated signal processing compared with the longitudinal magnetic recording system becomes required.